Marriage Authentication Affidavit

I am a American male engaged to a Chinese girl in Dalian. We want to marry in Dalian. According to the Dalian marriage office I need a marriage affidavit with my State Secretary of State notarized and a Chinese Seal of authentication.
The official seal is what I cannot find how to get here in the USA. No one answers at the Consulate in Chicago or embassy in DC.

Does anyone know?